Internal intermediate pressure 2-stage compression type rotary compressor

ABSTRACT

An internal intermediate pressure type two-stage compression rotary compressor ( 10 ) is provided with an electrically driven element ( 14 ) disposed within a sealed vessel ( 12 ), and first and second rotary compression elements ( 32, 34 ) driven by the electrically driven element ( 14 ), and is structured such as to discharge CO 2  refrigerant gas compressed at a first stage by the first rotary compression element ( 32 ) within the sealed vessel ( 12 ) and compress the discharged refrigerant gas having an intermediate pressure at a second stage by the second rotary compression element ( 34 ) via an accumulator ( 106 ). The rotary compression elements ( 32, 34 ) include upper and lower cylinders ( 38, 40 ), upper and lower rollers ( 46, 48 ) eccentrically rotating within the cylinder and upper and lower vanes ( 50, 52 ) brought into contact with the rollers so as to section the inner portions of the upper and lower cylinders into high pressure chambers and low pressure chambers. A ratio of volume between the upper and lower cylinders ( 38, 40 ) executing the compression operation at the first stage and the second stage is set to 1:0.65 so that an equilibrium pressure becomes equal to an intermediate pressure. 
     Since a pressure change at a time of starting is reduced, an oil foaming is restricted and it, is possible to easily employ a withstand pressure design of a sealed vessel, it is possible to easily design a withstand pressure vessel and it is possible to reduce a weight of the pressure vessel.

TECHNICAL FIELD

The present invention relates to an internal intermediate pressure typetwo-stage compression rotary compressor, and more particularly to aninternal intermediate pressure type two-stage rotary compressor, forexample, which can reduce a pressure change at a time of starting andcan reduce a weight of a pressure vessel.

BACKGROUND ART

In conventional, in a two-cylinder type two-state compression rotarycompressor in which an electrically driven element and two rotarycompression elements are arranged and received within a sealed vessel,the sealed vessel is used as an internal low pressure type of aninternal, intermediate pressure type.

In the case of the internal low pressure type, a refrigerant gas havinga low temperature and a low pressure and returning to an inner portionof the sealed vessel from an external refrigerant circuit constituting arefrigerant cycle via an accumulator is sucked from a suction passage soas to be compressed at a first stage by a first rotary compressionelement, and is thereafter fed out to an intermediate cooling devicepositioned at an external portion, thereafter the refrigerant gas havingan intermediate pressure is directly sucked to a second rotarycompression element by a refrigerant pipe and is further compressed at asecond stage, and the refrigerant gas having a high temperature and ahigh pressure is fed out to the external refrigerant circuit mentionedabove by the refrigerant pipe.

On the contrary, in the case of the internal intermediate pressure type,the refrigerant gas having the low temperature and the low pressure andreturning from the external refrigerant circuit constituting therefrigerant cycle via the accumulator is directly sucked to the firstrotary compression element by the refrigerant pipe, and is compressedhere so as to be discharged within the sealed vessel. Next, thedischarged refrigerant gas having the intermediate pressure iscompressed by the second rotary compression element so as to be fed outas the refrigerant gas having the high temperature and the high pressureto the external refrigerant circuit. That is, the pressure of therefrigerant gas discharged within the sealed vessel becomes theintermediate pressure between the first stage suction pressure and thesecond stage discharge pressure. Then, the intermediate pressure isdetermined on the basis of a bearing load, work loads in the respectivestages, and the like.

However, in the case that the intermediate pressure is lower than apressure (an equilibrium pressure) at a time when the compressor stops,a difference between the high pressure and the low pressure is lost andthe, pressure within the compressor becomes an equilibrium state, thepressure within the sealed vessel is rapidly reduced at a time ofstarting the compressor, the refrigerant lying up in the oil togethertherewith becomes bubbles and an oil foaming is generated. Further, inthe case that the intermediate pressure is higher than the equilibriumpressure, at a time when the compressor stops, the refrigerant gasrunning into the oil after starting becomes bubbles due to an increaseof temperature of the sealed vessel, whereby the oil foaming isgenerated. Further, in the case of using a CO₂ refrigerant, therefrigerant pressure reaches 100 kg/cm²G in a high pressure side, and30kg/cm²G in a low pressure side, and an amount of oil flowing out tothe low pressure side due to the pressure difference is increased.Further, it is necessary to apply any higher withstand pressure designamong that against the intermediate pressure and that against theequilibrium pressure to the sealed vessel.

Accordingly, a main object of the present invention is to provide aninternal intermediate pressure type two-stage compression rotarycompressor which can reduce a pressure change at a time of starting orthe like, can easily employ a withstand pressure design of a sealedvessel and can reduce a weight of the pressure vessel.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, there is provided an internalintermediate pressure type two-stage compression rotary compressorcomprising, an electrically driven element provided within a sealedvessel, first and second rotary compression elements driven by theelectrically driven element, CO₂ refrigerant gas compressed at a firststage by the first rotary compression element, being discharged withinthe sealed vessel and the discharged refrigerant gas having anintermediate pressure, being compressed at a second stage by the secondrotary compression element,

wherein a ratio of volume between the rotary compression element at thefirst stage and the rotary compression element at the second stage isset so that the equilibrium pressure becomes equal to the intermediatepressure.

The pressure change at a time of starting becomes small by setting theratio of volume of the rotary compression elements executing the firstand second stages of compression to a range between 1:0.5 and 1:0.8,whereby it is possible to restrict the oil foaming from being generated.Further, the withstand pressure design standard becomes 7000 kPa whichis substantially equal to the equilibrium pressure, and becomes a valueequal to that of the internal low pressure type.

The object mentioned above, the other objects, features and advantagesof the present invention will be further apparent on the basis of thefollowing detailed description of an embodiment given with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross sectional view of a main portion of aninternal intermediate pressure type two-stage compression rotarycompressor corresponding to an embodiment in accordance with the presentinvention;

FIG. 2 is a schematic view showing another embodiment of a terminal postportion in FIG. 1; and

FIG. 3 is a schematic cross sectional view of a main portion inrespective compression portions in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

An internal intermediate pressure type two-stage compression rotarycompressor 10 corresponding to an embodiment in accordance with thepresent invention shown in FIG. 1 includes a cylindrical sealed vessel12 made of a steel plate, an electrically driven element 14 arranged inan upper space within the sealed vessel 12, and a rotary compressionmechanism 18 positioned in a lower portion of the electrically drivenelement and driven by a prank shaft 16 connected to the electricallydriven element 14.

Further, the sealed vessel 12 has an oil storage for a lubricating oilformed in a bottom portion, and is constituted by two members comprisinga vessel main body 12A receiving the electrically driven element 14 andthe rotary compression mechanism 18 and a lid body 12B closing an upperopening of the vessel main body 12A. A terminal post 20 (a wire isomitted) for supplying an external electric power to the electricallydriven element 14 is mounted to the lid body 12B. In this case, theterminal post 20 is structured such that a main body portion 20A isformed in a flat surface shape as illustrated, however, in the case thatthe sealed vessel 12 is of an internal intermediate pressure or aninternal high pressure, a deformation of the main body portion 20A ishard to be generated by protruding a shape of the main body portion 20Aupward so as to form a curved surface shape as shown in FIG. 2, wherebya strength of the terminal post 20 is improved.

The electrically driven element 14 is constituted by a stator 22annularly mounted along an upper inner peripheral surface of the sealedvessel 12, and a rotor 24 arranged in an inner side of the stator 22with a slight gap. A crank shaft 16 extending in a vertical directionpassing through a center of the rotor 24 is fixed to the rotor 24. Thestator 22 has a layered body 26 obtained by laminating ring-likeelectromagnetic steel plates, and a plurality of coils 28 wound aroundthe layered body 26. Further, the rotor 24 is also an alternatingcurrent motor constituted by an electromagnetic steel plate layered body30 as in the same manner as that of the stator 22. Further, it ispossible to form as a DC motor in which a permanent magnet is inserted.

The rotary compression mechanism 18 includes a first rotary compressionelement 32 executing a compression at a first stage (in a low stageside) and a second rotary compression element 34 executing a compressionat a second stage (in a high stage side). That is, it is constituted byan intermediate partition plate 36, upper and lower cylinders 38 and 40respectively arranged in an upper side and a lower side of theintermediate partition plate 36, upper and lower rollers 46 and 48connected to upper and lower eccentric portions 42 and 44 of the crankshaft 16 and rotating within the upper and lower cylinders 38 and 40,upper and lower vanes 50 and 52 brought into contact with the upper andlower rollers 46 and 48 so as to respectively section inner portions ofthe upper and lower cylinders 38 and 40 into low pressure chambers 38 aand 40 a and high pressure chambers 38 b and 40 b, and an uppersupporting member 54 and a lower supporting member 56 closing upper andlower openings of the upper and lower cylinders 38 and 40 and commonlyserving as a bearing of the crank shaft 16 (refer to FIG. 3).

Discharge sound absorbing chambers 58 and 60 suitably communicating withthe respective high pressure chambers of the upper and lower cylinders38 and 40 are formed in the upper supporting member 54 and the lowersupporting member 56, and opening surfaces of the respective soundabsorbing chambers are closed by an upper plate 62 and a lower plate 64.

Further, as shown in FIG. 3, the upper and lower vanes 50 and 52 arearranged in radially disposed guide grooves 66 and 68 formed in cylinderwalls of the upper and lower cylinders 38 and 40 so as to freelyoscillate and slide, and are urged by springs 70 and 72 so as to bealways brought into contact with the upper and lower rollers 46 and 48.Further, in the upper cylinder 38, a compression operation at the firststage is executed, and in the lower cylinder 40, the compressionoperation at the second stage is executed by sucking the refrigerant gascompressed by the upper cylinder 38.

In this case, in order to keep the inner portion of the sealed vessel 12under an equilibrium pressure, that is, the intermediate pressure equalto the pressure at a time when the compressor stops, a differencebetween the high and low pressures is lost and the pressure within thecompressor becomes an equilibrium pressure, a ratio of volume betweenthe rotary compression element 32 at the first stage and the rotarycompression element 34 at the second stage is set to a range between1:0.56 and 1:0.8. In this embodiment, the ratio of volume is set to1:0.65.

For example, in the case that inner diameters of the upper and lowercylinders 38 and 40 are equal to each other, it is possible tocorrespond by changing a height (a thickness) thereof. That is, a heightof the roller 48 in the lower cylinder at the second stage is madesmaller than that of the roller 46 in the upper cylinder 38 at the firststage. Otherwise, in the case that the heights of the upper and lowercylinders 38 and 40 are equal to each other, an outer diameter of thelower roller 48 is made larger than an outer diameter of the upperroller 46 by changing the outer diameters of the upper and lower rollers46 and 48. In a particular method, it is possible to easily correspondby changing the outer diameter of the roller and an amount ofeccentricity in the eccentric portion.

In this case, a description will be given of a value of the ratio ofvolume. As a result of experimenting under a condition of the ratio ofvolume 1:0.55, the intermediate pressure becomes 80 kgf/cm², theequilibrium pressure becomes 60 kgf/cm² and the intermediate pressure >the equilibrium pressure is established. Accordingly, if the ratio ofvolume at the second stage is increased, it is assumed that theintermediate pressure is reduced, so that the value 0.8 corresponds toan upper limit value for functioning as the two-stage compressor.

Further, a material of the upper roller 46 and the upper vane 50constituting the rotary compression element 32 at the first stage ismade different from a material of the lower roller 48 and the lower vane52 constituting the rotary compression element 34 at the second stage.That is, a roller (a monicro: a Ni, Cr and Mo alloy additive wearresisting cast iron) and a vane (SKH: a high speed tool steel) made of asoft and inexpensive material are used in the upper cylinder 38 at thefirst stage having a small compression load, and a roller (an alloytarkalloy: a Ni, Cr, Mo and Bo alloy additive wear resisting cast iron)and a vane (PVD treatment: vacuum depositing a chrome nitride CrN on asurface of an SHK base material) made of an expensive and hard materialare used in the lower cylinder 40 at the second stage having a largecompression load, whereby it is possible to achieve a high durabilityand a cost reduction. Examples of the combination mentioned above willbe shown below.

ROLLER MATERIAL VANE MATERIAL FIRST STAGE MONICRO SHK SECOND STAGETARKALLOY PVD TREATMENT

Then, the upper supporting member 54, the upper cylinder 38, theintermediate partition plate 36, the lower cylinder 40 and the lowersupporting member 56 which constitute the rotary compression mechanism18 mentioned above are arranged in this order, and are connected andfixed together with the upper plate 62 and the lower plate 64 by using aplurality of mounting bolts 74.

In a lower portion of the crank shaft 16, a straight oil hole 76 isformed in an axial center, and spiral oil supplying grooves 82 and 84connected to the oil hole 76 via oil supplying holes 78 and 80 in alateral direction are formed on an outer peripheral surface, whereby thestructure is made such as to supply the oil to the bearing in the uppersupporting member 54 and the lower supporting member 56 and therespective sliding portions.

In this embodiment, as a used refrigerant, taking into consideration aglobal environment, a combustibility, a toxicity and the like, a carbondioxide (CO₂) corresponding to a natural refrigerant is employed, andthe oil corresponding to a lubricating oil employs an existing oil, forexample, a mineral oil, an alkyl benzene oil, an ester oil and the like.

Further, refrigerant suction passages (not shown) for introducing therefrigerant and refrigerant discharge passages 86 and 88 for dischargingthe compressed refrigerant are provided in the upper and lower cylinders38 and 40. Further, refrigerant pipes 98, 100, 102 and 104 are connectedto the respective refrigerant suction passages and refrigerant dischargepassages 86 and 88 via connection pipes 90, 92, 94 and 96 fixed to thesealed vessel 12. Further, an accumulator 106 is connected to a portionbetween the refrigerant pipes 100 and 102. Further, a discharge pipe 108communicating with the discharge sound absorbing chamber 58 of the uppersupporting member 54 is connected to the upper plate 62, whereby thestructure is made such as to directly discharge a part of therefrigerant gas compressed at the first stage into the sealed vessel 12and thereafter flow together with the remaining refrigerant gasdischarged from the refrigerant discharging passage 86 in a branch pipe110 connected to the refrigerant pipe 100.

Next, a description will be given of a summary of an operation of theembodiment mentioned above.

At first, when applying an electric current to the coil 28 of theelectrically driven element 14 via the terminal post 20 and the wire(not shown), the rotor 24 rotates and the crank shaft 16 fixed theretorotates. Due to the rotation, the upper and lower rollers 46 and 48connected to the upper and lower eccentric portions 42 and 44 integrallyprovided with the crank shaft 16 eccentrically rotate within the upperand lower cylinders 38 and 40. Accordingly, the refrigerant gas suckedto the low pressure chamber 38 a of the upper cylinder 38 from thesuction port 112 as shown in FIG. 3 via the refrigerant pipe 98 and therefrigerant suction passage (not shown) is compressed at the first stagein accordance with the operation of the upper roller 46 and the uppervane 50. Further, a part of the refrigerant gas having the intermediatepressure and discharged to the discharge sound absorbing chamber 58 ofthe upper supporting member 54 from the high pressure chamber 38 b via adischarge port 114 is discharged within the sealed vessel 12 from thedischarge pipe 108, and the rest thereof is fed out to the refrigerantpipe 100 through the refrigerant discharge pipe 86 of the upper cylinder38 so as to flow together with the refrigerant gas flowing therein fromthe branch pipe 110 in the middle thereof and discharged within thesealed vessel 12.

Next, the refrigerant gas after combination flows to the refrigerantpipe 102 via the accumulator 106, and the refrigerant gas having theintermediate pressure and sucked to the low pressure chamber 40 a of thelow cylinder 40 from a suction port 116 shown in FIG. 3 via therefrigerant suction passage (not shown) is compressed at the secondstage in accordance with the operation of the lower roller 48 and thelower vane 52. Further, the high pressure refrigerant gas discharged tothe discharge sound absorbing chamber 60 of the lower supporting member56 from the high pressure chamber 40 b of the lower cylinder 40 via adischarge port 118 is fed out to an external refrigerant circuitconstituting the refrigerant cycle from the refrigerant dischargepassage 88 through the refrigerant pipe 104. Thereafter, the suction,compression and discharge operation of the refrigerant gas is executedon the basis of the same passage.

Further, due to the rotation of the crank shaft 16, the lubricating oil(not shown) stored in the bottom portion of the sealed vessel 12 ascendsthrough the oil hole 76 extending in the vertical direction and formedin the axial center of the crank shaft 16, and flows out to the spiraloil supplying grooves 82 and 84 formed on the outer peripheral surfacethereof by the oil supplying holes 78 and 80 provided in the middlethereof in the lateral direction. Accordingly, it is possible to wellsupply the oil to the bearing of the crank shaft 16, the respectivesliding portions of the upper and lower rollers 46 and 48 and the upperand lower eccentric portions 42 and 44, so that the crank shaft 16 andthe upper and lower eccentric portions 42 and 44 can smoothly rotate.

In this case, it is possible to reduce an increase of temperature of thesuction refrigerant gas by forming the refrigerant pipes 90 and 94connected to the respective refrigerant suction passages of the upperand lower cylinders 38 and 40 in a double-pipe shape or applying a heatinsulating agent to an inner wall of the refrigerant pipe, whereby asuction efficiency can be improved. Further, the same effect can beobtained by forming the refrigerant suction passage itself in adouble-pipe shape or applying a heat insulating agent to an inner wallof the passage pipe.

INDUSTRIAL APPLICABILITY

In accordance with the present invention, since it is possible torestrict the generation of the oil foaming at a time of starting, it ispossible to prevent the oil formed in a foam shape within the sealedvessel from flowing within the cylinder together with the refrigerantgas, and being thereafter discharged out of the compressor, so that itis possible to prevent an oil shortage within the sealed container.Further, it is possible to easily employ a withstand pressure design ofa sealed vessel and it is possible to reduce a weight of the pressurevessel. As a result, a performance of the compressor can be improved anda cost can be reduced.

What is claimed is:
 1. An internal intermediate pressure type two-stagecompression rotary compressor comprising: an electrically driven elementprovided within a sealed vessel; first and second rotary compressionelements driven by said electrically driven element; CO₂ refrigerant gascompressed at a first stage by said first rotary compression element,being discharged within said sealed vessel; and the dischargedrefrigerant gas having an intermediate pressure, being compressed at asecond stage by said second rotary compression element, wherein a ratioof volume between the rotary compression element at the first stage andthe rotary compression element at the second stage is set so that theequilibrium pressure becomes equal to the intermediate pressure.
 2. Aninternal intermediate pressure type two-stage compression rotarycompressor as claimed in claim 1, wherein said ratio of volume is set toa range between 1:0.5 and 1:0.8.
 3. An internal intermediate pressuretype two-stage compression rotary compressor as claimed in claim 2,wherein said ratio of volume is set to 0.65.
 4. An internal intermediatepressure type two-stage compression rotary compressor as claimed inclaim 2, wherein said respective rotary compression elements include acylinder, a roller eccentrically rotating within said cylinder and avane brought into contact with said roller and sectioning said cylinderinto a high pressure chamber and a low pressure chamber, and said ratioof volume between the first stage and the second stage is set to apredetermined range by changing a height of said cylinder.
 5. Aninternal intermediate pressure type two-stage compression rotarycompressor as claimed in claim 2, wherein said respective rotarycompression elements include a cylinder, a roller eccentrically rotatingwithin said cylinder and a vane brought into contact with said rollerand sectioning said cylinder into a high pressure chamber and a lowpressure chamber, and said ratio of volume between the first stage andthe second stage is set to a predetermined range by changing a diameterof said roller and an amount of eccentricity of the crank shaft.
 6. Aninternal intermediate pressure type two-stage compression rotarycompressor as claimed in claim 4 or 5, wherein a material of the rollerand the vane constituting the rotary compression element at said firststage is made different from a material of the roller and the vaneconstituting the rotary compression element at said second stage.
 7. Aninternal intermediate pressure type two-stage compression rotarycompressor as claimed in claim 6, wherein the material of the roller andthe vane at said second stage is harder than the material of the rollerand the vane at said first stage.